backport of bug #54476 fix from 5.1-bugteam to 5.0-bugteam.
Original revid: alexey.kopytov@sun.com-20100723115254-jjwmhq97b9wl932l > Bug #54476: crash when group_concat and 'with rollup' in > prepared statements > > Using GROUP_CONCAT() together with the WITH ROLLUP modifier > could crash the server. > > The reason was a combination of several facts: > > 1. The Item_func_group_concat class stores pointers to ORDER > objects representing the columns in the ORDER BY clause of > GROUP_CONCAT(). > > 2. find_order_in_list() called from > Item_func_group_concat::setup() modifies the ORDER objects so > that their 'item' member points to the arguments list > allocated in the Item_func_group_concat constructor. > > 3. In some cases (e.g. in JOIN::rollup_make_fields) a copy of > the original Item_func_group_concat object could be created by > using the Item_func_group_concat::Item_func_group_concat(THD > *thd, Item_func_group_concat *item) copy constructor. The > latter essentially creates a shallow copy of the source > object. Memory for the arguments array is allocated on > thd->mem_root, but the pointers for arguments and ORDER are > copied verbatim. > > What happens in the test case is that when executing the query > for the first time, after a copy of the original > Item_func_group_concat object has been created by > JOIN::rollup_make_fields(), find_order_in_list() is called for > this new object. It then resolves ORDER BY by modifying the > ORDER objects so that they point to elements of the arguments > array which is local to the cloned object. When thd->mem_root > is freed upon completing the execution, pointers in the ORDER > objects become invalid. Those ORDER objects, however, are also > shared with the original Item_func_group_concat object which is > preserved between executions of a prepared statement. So the > first call to find_order_in_list() for the original object on > the second execution tries to dereference an invalid pointer. > > The solution is to create copies of the ORDER objects when > copying Item_func_group_concat to not leave any stale pointers > in other instances with different lifecycles. mysql-test/r/func_gconcat.result: Test case for bug #54476. mysql-test/t/func_gconcat.test: Test case for bug #54476. sql/item_sum.cc: Copy the ORDER objects pointed to by the elements of the 'order' array in the copy constructor of Item_func_group_concat. sql/table.h: Removed the unused 'item_copy' member of the ORDER class.
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